1. Technical Field
The present invention relates to technology for driving scan lines by using a demultiplexer.
2. Related Art
In electro-optical devices such as liquid crystals, pixels are provided in correspondence with a plurality of scan lines and a plurality of data lines. Each pixel has a gray scale level in accordance with a voltage value (or current value) of a data line corresponding thereto when a scan line corresponding thereto has an active level (for example, level H), and each pixel is configured to maintain the gray scale level thereafter even when the scan line has a non-active level (level L when the active level is level H). Thus, the plurality of scan lines are sequentially made to have the active level in a predetermined order, and voltages (or currents) in accordance with gray scale levels are supplied through data lines to the pixels positioned in a scan line which is made to have the active level, and thereby a target image can be displayed.
Here, a circuit that makes the plurality of scan lines to have the active level in a predetermined order is referred to as a scan line driving circuit, and generally, a shift register is used as the scan line driving circuit. Among the scan line driving circuits, a so-called peripheral circuit mounted type scan line driving circuit that is configured with same switching elements as the pixels instead of mounting an externally attachable integrated circuit has an advantage in view of improvement of production efficiency or the like by using a common manufacturing process.
However, since the shift register has a complementary type logic circuit (an inverter or a clock inverter) that combines a p-channel transistor and an n-channel transistor, when electrical characteristics are not configured as the p-channel type or the n-channel type, there is a problem that a penetration current flows.
Thus, a so-called demultiplexer type scan line driving circuit in which the scan lines are divided into blocks each having a plurality of lines (for example, three lines) and transistors (TFTs) are provided as switches in the scan lines, the blocks are sequentially selected one by one by using address signals, and switches of the plurality of scan lines belonging to the selected one block are sequentially turned on one by one by using selection signals, and thereby sequentially making the scan lines to have the active level has been proposed (for example, see JP-A-2002-169518 (particularly FIG. 1)).
However, when the above-described technology is used, a period of a high impedance (floating) state during which scan lines are not electrically connected to any part of the circuit in a non-selection period, in which the scan lines are not selected, may be relatively long. Here, in the high impedance state, when the electric potentials of the scan lines change due to a noise or the like, off-leaks in the pixels become different with each other. Accordingly, a stripe pattern in a row direction is generated on a display screen, and thereby deteriorating the display quality.